Power supply circuit with self-starting function

In some cases, it is necessary for electrical equipment to be put into operation immediately when power comes back after a power outage. In this case, the circuit as shown in the figure can be used .
    When self-starting is not required, open the switch SA; when self-starting is required, close SA. The self-starting function
is realized through R and C.
RP setting), VT3 is turned on after a short delay (due to the action of capacitor C2), so that VTz is turned on. At this time and during short circuit,
    in order to avoid instantaneous power incoming after power outage (such as the interval is less than
ls), the electrical equipment Frequent starts and stops will cause impact on the power grid and electrical equipment
, and the circuit should have a delay function. It is implemented in this way: after a power outage, the capacitor C
is discharged through the KA coil and R, so that KA can continue to maintain the pull- in for a period of time
. Appropriate selection of the parameters of R, C and KA can make the KA pull-in time
greater than Is.